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Re-boxing your T-Amp

Replace the plastic case--keep the realistic soundstage

[Italian version]

This is written for people who already have a T-Amp. If you are one of those who does not, then please read the other articles on TNT-audio about this revolutionary new amplifier. See our original review and recent comments by other users.

Learning to tweak the T-amp

Because this amp is so cheap and because the stock case, controls and connectors are so flimsy, the TNT reviews, the TNT forum and many other audio newsgroups on the web consider ways in which this amp can be modified. Much of this discussion is quite technical and aimed at experienced audio-tweakers. For example, there is an active discussion of this on www.diyaudio.com which includes suggested modifications to the PCB itself.

Beginners welcome

This article is written for audio beginner, who might like to join in the fun. It aims to give inexperienced people some practical guidance on how they can personalise their amp and make it more convenient to use. It assumes that you have, and know how to use, a few star (Philips) screwdrivers and a soldering iron (about 20W is fine), but not much more. For resoldering or making new joints you will need some electrical solder.
Optional extras are: desoldering wick or a desoldering pump (see picture 6 below) and some liquid electrical flux (e.g. Baker's Soldering Fluid No. 3).

If you follow the procedure described here, you can take some of the first steps in amp modification and learn skills that you can apply to other electronic repairs or kit building.

It's safe and fairly easy

The T-amp is an ideal amp to play with in this way. It is cheap enough to experiment with without risking too much if it all goes wrong, yet it is pretty tough. I have found the main board is quite forgiving of rough handling and clumsy soldering. And, it is reasonably safe to play with. It only uses a 12V power supply, so there are no dangerous voltages, or hot components inside it. Having said that, PLEASE be careful with that hot soldering iron, and DO NOT EVER plug this amp directly into a mains power supply. Only use batteries or one of the recommended power supplies. Okay, get yourself a couple of screwdrivers and let's get busy...

PART 1: TAKING IT APART

Looking at the amp from the outside

This is the T-Amp, straight from the box. All there is on the front is the combined on/off switch and volume control. The name for this is potentiometer, or "pot" for short. One of the modifications we will do is to replace this cheap component with two separate parts: an on/off switch and a good quality pot.

[T-Amp front]

The back of the amp has two sets of cheap clips for connecting thin speaker cables. The holes for these are very thin, so the second change we will make will be to replace these with standard speaker terminals which can take heavier cable with banana plug connections. Between the speaker connections are two other sockets. One is the socket for the 12V DC power supply (just 12V DC remember, no direct wiring to the mains supply) and the other is for a standard 3.5mm mini jack input of the kind found on portable CD or MP3 players or laptops. The supplied link is very basic, and should be replaced, even if you don't intend opening up your T-amp!

[T-Amp back]

Amazingly, most of the chassis space in the T-amp is taken up with space for the 8 AA batteries that can be used to power it. With the battery case opened, the amplifier itself can be seen (mounted upside down) through slotted vent between the two battery compartments.

[T-Amp underside]

Opening the chassis and detaching the switch and volume control

There are six screws to remove to open the chassis. The first four are hidden under the stick-on rubber footpads: just peel them off with your fingernail, or a sharp knife. They will stick back on, if needed. Then, inside the rear inside corners of the battery compartment are two more little screws. In the picture below, the small screwdriver points to them. Remove these two and the ease the chassis apart: don't force anything, wiggle a bit and it will come apart quite easily.

[Removing screws from chassis]

The picture below shows what you will see. At the top is the combined on/off switch and volume control, soldered to its own little printed circuit board (PCB). This is linked to the main PCB of the amp via a white connector linking two red wires to the on/off switch and a cable of five white wires to the volume control pot. The connector can be unclipped. Again, slide it apart carefully. This enables you to detach the top of the amp.

[Inside the case]

If you are planning to put your amp in a new chassis and case and replace the switch and volume pot, you can put the top away. You won't need it again, though you might try removing the switch/pot from its PCB to practice desoldering. Use a small thin screwdriver to lift off the plastic knob. Underneath, the pot is attached by three screws. Unscrew these to release the pot and board from the back of the chassis. Now you can practice desoldering with this, using a pump, or desoldering wick. These are illustrated in the pic below.

[Desoldering braid and pump]

Detaching and desoldering the speaker clips

While the on/off switch and pot is flimsy, it works okay, but the speaker clips are cheap and nasty. They have to go! They are just clipped to the inside of the amp. To release each one, press one side of the clip in firmly with your thumb, while supporting the back with your other fingers, and you will be able to slide one side out. The rest of the clip will now come out of the back easily.

[Removing the speaker clips]

You can now desolder the red and black wires from each clip. Note that there is a small capacitor soldered between each pair. Desolder these carefully, and remember to reconnect them in the same way to your new speaker connections. As you desolder the speaker wires, it is worth attaching a small tag to each one (L Spkr, R spkr, etc) to remind you of where it belongs. Keep the small brown caps to use later and toss the speaker clips away. You won't need these again!

Desoldering the two battery power input wires

Looking at the chassis from below, there is one black and one red wire still attached. These are the power leads from the batteries. The T-amp does not perform best with batteries, so there is little point in retaining the battery container. You will need the battery wires to attach to a separate power input jack, so desolder each one carefully, or snip them free just beyond the solder joint to the chassis.

Removing the main PCB from the original chassis

All that now secures the main PCB to the chassis is some glue sticking it to either side of the battery containers and two black spots of melted plastic where it has been heat-bonded to the chassis. This is where you need to be careful. Like all printed circuit boards this one should be handled gently. Try not to scratch or bend it. If you snap it, it's finished. But don't worry, because it's small, it's tough.

Use a craft knife to cut the glue attaching the PCB to the sides of the battery holder. Then use your soldering iron to melt the two black plastic spots which are all that now still attaches the board to the chassis. Be gentle with this. It will come away, but don't force anything. When the board is loose, draw it away from the back of the chassis and the DC12V and Audio Input sockets will slide out. If there is a dab of glue there too, ease the craft knife in to detach it.

Congratulations, you've now detached the pcb successfully! You are half-way with your project.

PART 2: PUTTING IT ALL BACK TOGETHER, BETTER THAN NEW

Now we can start putting this tiny board into a flashy and/or sturdy new case and replacing the components we have removed with good quality items. This second part will describe what I did with my first T-amp. It is just one worked example of what can be done.

Getting what you need together

At this point you will need to locate an electronics parts supplier to get the good quality replacements parts that you will need. If you get stuck with this, why not join the TNT Discussion Forum and ask for help? Go to our main page for information on how to do this.

For a new case, I chose a small wooden box from the home decorating department of a department store. I put it on its side with four rubber feet at the bottom and, hey-presto, a new case for about £5. The brand name of the box is Boom, so it's my own personal Boom Box. I like the heavy metal front, but it has been a pain to work with, especially with getting access to components mounted at the back, so you might prefer to buy a proper plastic enclosure from a supplier like Maplins. They do some nice translucent ones in ice-blue or infra red plastic, as well as ones in aluminium etc. None are very expensive.

A new switch: Any electrical shop will sell you a little toggle switch like the one I used. But, any simple on/off switch will do.

A new pot: If you plan to use your amp as an integrated amp, you will need a new pot. The value I used is 50k as this is the value of the pot reported by most tweakers, and because it worked okay with an old one I had with this value.   I bought a new high quality audio-grade one made by Alps. It cost me £14—half the cost of the original amp!—from a UK audio kit supplier, but I have seen them for much less on the net, and you can buy other quality makes which are much cheaper too.

New speaker terminal posts: These can be bought singly (two reds and two blacks) or in pairs. I already had some cheap ones to use, all in red, so I coloured two of them black myself! You can buy nice ones in red and black easily from mail order suppliers of electronic components. Just type "speaker terminal posts" with the name of your country into a search engine.

New phono chassis sockets: The basic ones are very cheap, or you can splash out on gold plated ones… Again, any major supplier will have these.

I have also added a separate DC input jack at the rear. This is because the board is a bit shorter than the width of my box, and I wanted to just poke the existing LED on the board through a hole in the front. This is not really elegant. It would be easier to use a separate LED (light emitting diode). These are very cheap and also available from electronics suppliers. Snip off the existing one close to the end and solder a new one to the pins. These only work one way, so if it does not light up, you will need to switch it round. This is the only part of this report that I have not yet done myself.

What I did is this:

[Inside the new box]

The first step is to plan where you will locate your pot and switch on the front, and where to locate the speaker posts, phono sockets and DC input jack. There is no law that says that they have to be on the front or back. You could be playful or creative.

I located the pot and switch in the front, because there were already two holes in the metal "lid" where the handle was attached. My phono sockets are widely separated because I began by just using the 3.5mm mini jack on the board and needed a large hole to insert it at first!

Having decided where you want to locate the components, drill all the holes at this stage, to avoid the hassle of making these adjustments once some of the connections have been made.

Once the holes are sorted you can attach the components. Think about preparing them to receive soldered attachments. Because my new case is a wooden box, and I had to solder some connections together in this confined space, I put a spot of flux and solder on the points to be soldered before fixing the components onto the back of my box. Then I was able to join them with a quick touch of heat and solder later.

Most of the components just screw into holes. With the pot and the switch you will need to make an additional small hole or indent alongside the main holes where the pins that stops these rotating around are inset. Looking at the pot from the front with the pins up, you can see this pin on front to the right hand side.

[Wiring the new volume control]

Wiring the pot to the main PCB

To connect your new pot to the main board you will have to cut off the white connector cable. But do this one strand at a time. First, cut loose the two red wires. Ignore them for now. They are for the on/off switch.

Place the board down with the LED pointing towards you. The white connecting block now has the two red wires at the bottom with five wires above it.

Place the pot down securely (stick it to your work surface with blu tack if you have it), with the control post towards you and the pins facing upwards, as in the picture below. With this orientation, I describe these pins as front L, front centre, front R, back L, back centre and back R.

Now one by one, cut the white wires free and solder them to the pot in this order, starting with the one nearest the red wires. I number these 1-5 from the red wires.

Wire 1 goes to the back centre (to volume from R channel)

Wire 2 goes to front centre (to volume from L channel)

Wire 3 goes to back R. You will also need to solder a short wire from back R to front R, as I have done in brown (should be in green, as this goes to ground!)

Wire 4 goes to front L (from volume control to amp L channel)

Wire 5 goes to back L (from volume control to amp R channel)

And, yes, it would have been easier if these had been different colours! But the arrangement is still logical, if you think about it.

Don't attach the volume pot to your case yet, but when you do you will need a knob to turn the control post easily. These fasten with a screw or via an allen key screw. Kevin and Ed at Salisbury HiFi gave me the one in the picture—thanks guys.

Wiring the switch to the PCB

Wiring up the new switch is easy. With a simple toggle switch, attach one red wire to the middle one pin and the other to either end.

[Wiring the new power switch]

Wiring the speaker posts to the PCB

When desoldering the speaker clips, you marked them L spkr and R spkr, didn't you? Good. Now you need to resolder each of the four cables: for the left hand speaker one red and black cable, with the small brown cap bridging them, and the same on the right hand side. As I say, this was a fiddly job for me, working inside this box, so think about this when choosing your case.

[Wiring the new speaker posts]

Wiring the phono sockets to the PCB

There are two ways of doing this, the neat but hard way or the easy way.

The hard way involves desoldering the mini jack connector from the board. This takes patience but can be done. In the picture below, the red LED is at the bottom.

[Wiring the new phonos to the PCB]

Once the connector has been removed, you connect the phono sockets like this:

  1. Solder the central earth pin (designated "E" in the picture) to the outer tag of each phono socket.
  2. Solder the centre pin of the R input phono socket (usually marked in red) to the hole designated "R".
  3. Solder the centre pin of the L socket to the hole designated "L".

You don't have to remove the phono connector board though. You can solder the connections to the underside of the board instead.

Turn the board upside down. With the red LED nearest to you, the input pins are now at the top left.

The earth pin is the first soldered pin in the top left corner. Connect this to the outer tag of each phono socket.

Second, working from the top left corner, find the first pin down the left hand side of the board, and solder a connection from there to the centre pin of the R (red) phono connector.

Third, work inwards from the left count skip two soldered pins and solder a cable from there to the centre pin of the L (white) phono connector.

When making these last two connections to the pcb, be careful not to make a solder bridge between them and the pins beside them.

As I said earlier, try and choose a case which makes it easy to make these soldering connections.

Wiring up the DC jack

The last connection to be made is the 12V DC power input jack. This is the connector to an external 12V power source. If you don't have one, you can order one (either model HP143 or HP145) from these suppliers: www.zgitaly.it/ The site gives details of regional distributors. Some people report good results with even bigger power supplies, e.g. 7A 13.8V DC!

Remember the red and black battery wires you cut free? Well, these are what you connect to the input jack. The red wire should be connected to the inside pin and the black to the outside one. This polarity is important!

[Wiring the new DC jack]

Put it all back inside and switch on

And... well, that's it folks. Before you close up the case, double-check that all the connections are secure and accurate. It's easy to make a mistake and thin wires can come loose as you work.

If all is connected up as described above you will find that it is a pleasure to connect the amp to a quality audio source (e.g. CD player) and speakers. The first time you plug in the power supply the switch might on the on position so turn the pot to a middle position before you switch on: these amps may be small, but they can go quite loud.

[New case rear view]

[New case side view]

© Copyright 2005 David Holgate - www.tnt-audio.com

HTML: Tom Browne

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